Let's solve this addition problem. We have 3621 and 4172, and we need to add them together.

Step 1: We'll start by adding the digits 1 & 2 in column 1 and get 3.

Step 2: We'll start by adding the digits 2 & 7 in column 2 and get 9.

Step 3: We'll start by adding the digits 6 & 1 in column 3 and get 7.

Step 4: We'll start by adding the digits 3 & 4 in column 4 and get 7.

So, 3621 + 4172 = 7793.

